This invention relates generally to turbocharger systems for use with combustion engines. More specifically, this invention relates to an improved hydraulic assist turbocharger system and related control arrangement for use in controlling the operation of an hydraulic assist turbocharger, such as that described in U.S. Pat. Nos. 4,285,200 and 4,444,014.
Turbochargers and turbocharger systems are generally known in the art for supplying a combustion engine with a charge of air under pressure, commonly referred to as charge air. The turbocharger typically comprises a turbine wheel and a compressor wheel mounted for rotation with a common shaft. The turbine wheel and the compressor wheel are positioned respectively within turbine and compressor housings, which are mounted in turn at the opposite ends of a so-called center housing including appropriate shaft bearings for supporting the rotating shaft. Exhaust gases from a combustion engine are coupled for passage through the turbine housing to rotatably drive the turbine wheel, whereby the rotating turbine wheel correspondingly drives the compressor wheel to draw in and compress ambient air for supply as charge air to the intake manifold of the combustion engine.
Turbocharged engines are highly advantageous when compared with conventional naturally-aspirated engines in that substantially denser air is delivered to the combustion chamber or cylinders of the engine. This increased air density results in an increased mass flow of available air for combustion, thereby permitting the engine to operate at substantially higher performance levels and/or with greater efficiency However, an inherent limitation with turbochargers has been their inability to provide the engine with sufficient charge air during some conditions of engine operation. For example, charge air supplied to the engine by the turbocharger during low speed operating conditions is typically insufficient to permit engine operation at a relatively high load and/or to permit relatively rapid engine acceleration. Moreover, in a two-cycle engine, charge air supplied by the turbocharger during starting and/or other low speed operating conditions is normally insufficient to keep the engine from stalling.
A variety of system concepts are known in the art for boosting or supplementing the normal charge air output of a turbocharger during selected engine operating conditions. For example, auxiliary combustion systems have been proposed to supplement the energy level of the engine exhaust gases during selected engine operating conditions. Compound turbocharger systems have also been proposed wherein multiple turbine and/or compressor components are interconnected to provide supplemental charge air. Additional system concepts include, for example, mechanical drive trains for mechanically supplementing turbocharger rotation, and hydraulic drive systems for hydraulically supplementing turbocharger rotation.
One system concept of particular note is described in detail in U.S. Pat. No. 4,285,200 and comprises a specific hydraulic drive arrangement in the form of a so-called three-wheeled turbocharger. In this system, a nonventilated hydraulic turbine is carried on a turbocharger shaft between the turbine and compressor wheels, and this nonventilated hydraulic turbine is supplied with hydraulic fluid under pressure to supplementally drive the turbocharger. In this manner, the mass flow output of charge air for supply to the engine is significantly increased during selected operating conditions. However, successful operation of this type of hydraulic drive system is predicated upon provision of an efficient control arrangement for rapidly supplying the hydraulic turbine with a regulated flow of pressurized hydraulic fluid in accordance with an engine air flow requirement schedule. Moreover, it is highly desirable for the control arrangement to unload hydraulic pumping elements when the need for supplemental driving is reduced or not required, such that parasitic hydraulic power losses can be minimized.
An improved hydraulic drive arrangement for a three-wheeled turbocharger is described in U.S. Pat. Nos. 4,444,014 and 4,478,043. In this improved system, hydropneumatic control valve components are provided to regulate flow of hydraulic fluid to an hydraulic assist turbine in a turbocharger. This hydropneumatic control scheme responds to engine speed and load parameters to unload the hydraulic pumping elements in a progressive manner, when pumping capacity otherwise exceeds the need for supplemental driving of the turbocharger. However, this type of control arrangement lacks the flexibility and broad control range required to provide adequate supplemental driving of the turbocharger during some conditions of operation, particularly such as low speed and/or starting conditions wherein supplemental driving requirements may be independent of engine speed and load.
The present invention provides an improved hydraulic assist turbocharger system having control components adapted to provide a regulated or scheduled flow of pressurized hydraulic fluid to the hydraulic turbine of a three-wheel turbocharger, wherein this fluid flow is controlled in response to engine air requirements which may be substantially independent of engine speed and load parameters.